The present invention relates to a nonrecursive half-band filter. A half-band filter exhibits an amplitude frequency response which is symmetrical with respect to the 50%-attenuation point occurring at a quarter of the sampling rate fA (see FIG. 2A).
Nonrecursive digital filters are discussed in general by Samuel D. Stearns, "Digital Signal Analysis," chapter 8 (entitled "Nonrecursive Digital Systems," pages 102-119), 1975. Furthermore nonrecursive half-band filters are disclosed by Maurice G. Bellanger et al in an article entitled "Interpolation, Extrapolation, and Reduction of Computation Speed in Digital Filters," IEEE Transactions on Acoustics, Speech and Signal Processing, Volume ASSP-22, No. 4, August 1974, pages 231-235. These prior half-band filters process real input signals into real output signals.